Sebastian Vettel does not understand why he was so far off the pace in Thursday practice at Monaco, but is hopeful Red Bull can understand the issue by qualifying on Saturday.

Vettel was ninth fastest and over a second off Nico Rosberg at the top of the timesheets after failing to improve on his super-soft tyre lap. He said he opted to make a set-up change during the second session and that lost him time.

"All in all it was okay, but unfortunately we had to make a big change and we lost quite a lot of time in the afternoon," he said. "Not completely ideal but that's Friday - or in this case Thursday. We'd like to be more competitive in low-fuel configuration, so we need to try and find some lap time there.

Vettel added that the car seemed better over long runs.

"My run on super-soft was very poor and we need to understand why. I wasn't able to improve and we should be able to quite easily so we need to have a look. After that I did a long-run on super-softs and it seemed quite okay."